1. Technical Field
The present disclosure relates to an elapsed-time determination apparatus that determines elapsed time after death of a fish based on an image of the fish, a deciding apparatus, a deciding method, and a non-transitory computer-readable recording medium storing a control program.
2. Description of the Related Art
Japanese Patent No. 4291381 discloses a method of judging freshness of edible fish using a K value. The K value is an index of freshness that takes advantage of the fact that adenosine triphosphate (ATP) in muscle tissue of a living body breaks down after death of the organism, and further changes from inosine monophosphate to hypoxanthine. That is to say, the K value is a percentage expression of the total amount of inosine and hypoxanthine as to the total amount of adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, inosine monophosphate, inosine, and hypoxanthine. Fresh fish includes large amounts of adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, and inosine monophosphate. Fish which have lost freshness due to time having elapsed after death include large amounts of inosine and hypoxanthine. Accordingly, the smaller the K value is, the fresher the fish is.
EP Patent Application No. 2189789 discloses a method of determining an amount of time elapsed after death, using a boundary position between the pupil portion of the eye and the surrounding white portion by image processing based on an image of the fish. This method takes advantage of the fact that the boundary position between the pupil and the white changes over time after death.
The K value is obtained by directly measuring chemical substances contained in the flesh of fish that are deeply related to freshness, so the K value is a precise indicator of the freshness of the fish flesh. However, measurement of the chemical substances contained in the flesh of fish is conducted by extracting flesh from the fish. That is to say, obtaining a K value necessitates marring the merchandise that is the fish, meaning that obtaining the K value reduces the value of the merchandise.
Further, judgment of the freshness using the boundary position between the pupil and the white is affected by differences such as the type of the fish, for example. Accordingly, there may be cases where the boundary positions cannot be appropriately identified, and judging freshness becomes difficult.